In multi-carrier wireless communication systems, such as mobile phone networks, wireless local area networks and satellite communications, transmitters and receivers communicate through wireless propagation “channels.” The transmitted waveforms are reflected by scatterers present in the wireless media, and arrive at the receiver via many different paths. The multi-path wireless channel causes interference between the transmitted data symbols, referred to as inter-symbol interference (ISI).
In order to recover the transmitted sequence, the receiver estimates and compensates for the channel effects induced by the wireless communication channel. The channel is characterized either in the time-domain via its impulse response (the channel output when the input is an impulse), or in the frequency domain via its frequency response (the channel output when the input is a complex exponential with certain frequency). Techniques for estimating the channel's impulse or frequency response are generally referred to as data-aided, blind, or, semi-blind. In data-aided techniques, the transmitter sends a training sequence that is known by the receiver. The receiver can then estimate the impulse response of the channel by comparing the received data, i.e., the output of the channel, with the training sequence. In blind and semi-blind techniques, the receiver applies advanced signal processing algorithms to estimate the channel effects without exact knowledge of the transmitted data.